Fine-structural and functional aspects of the cerebrospinal fluid-contacting subependymal cells in the anuran hypothalamus.

Cytological characteristics of the cerebrospinal fluid (CSF)-contacting subependymal cells in the frog hypothalamus were investigated to decide whether they should be classified as neurons, sensory cells or secretory (endocrine) cells. The CSF-contacting subependymal cells exhibited morphological characteristics similar to neurons or sensory cells, which are usually supplied with axo-somatic and -dendoritic synapses from other neurons and possess somato-dendritic synapses to other neurons. Furthermore, they were provided with so-called sensory cilia. The CSF-contacting subependymal cells also exhibited several cytological secretory cell characteristics: the presence of numerous secretory granules, well-developed granular endoplasmic reticulum and Golgi apparatus in the perikaryon as well as intraventricular processes, and some figures which may be regarded as microapocrine or diacrine secretions of the secretory granules. Furthermore, the CSF-contacting subependymal cells probably sent basal cell processes to the area around the blood vessels in the neurohypophysis and, perhaps, in the infundibulum. It seemed likely that CSF-contacting subependymal cells had two or three functions of a paraneuronic nature. They were sensory to chemical or physical stimuli frmones just as endocrine cells do.